Low temperature grease compositions



Patented June 1, 1954 LOW TEMPERATURE GREASE COMPOSITIONS Bruce W. Hotten, Orinda, and Robert J. Houston,

San Rafael, Calif., assignors to California Research Corporation, San Francisco, Calif., a

corporation of Delaware No Drawing. Application September 15, 1951, Serial No. 246,872

15 Claims. 1

This invention pertains to grease compositions which are plastic at extremely low temperatures, such grease compositions containing a soap thickened base oil comprising essentially a mixture of a polyether oil and a polysiloxane oil.

During recent years, it has been a major problem of the lubricating industry to prepare greases which would afford the desired lubrication at extremely low temperatures (e. g., 100 F.) and not become too fluid or too volatile at high temperatures (e. g. 250 F.). Greases which are plastic at low temperatures as well as at high temperatures are useful in such severe variations of weather conditions as are encountered in the operation of airplanes, in the operation of military equipment in extreme cold weather and hot weather, etc. It is extremely advantageous to be able to use one grease composition which is plastic at low and high temperatures, and which is further characterized by high resistance to oxidation, heat stability, etc.

In the preparation of grease compositions using only petroleum base oils, when the greases are suitable at the low temperatures, they normally become too volatile at the high temperatures; and when the greases are suitable at high temperatures, they become too stiff or too solid at low temperatures. Even when the petroleum oils have been as highly refined as possible to increase the viscosity index to its maximum, it has been impossible to prepare greases which give adequate lubrication at extremely low and high temperatures.

Numerous synthetic oils have been prepared in recent years to satisfy certain requirements in the lubrication field. For example, polysiloxane oils can be used as lubricating oils under extremely warm or cold conditions. Heretofore, it has been diiiicult to form grease compositions from a polysiloxane oil because the grease thickening agents normally used are difiicultly dispersible in the polysiloxane oils.

Similarly, polyether oils are synthetic base oils which normally are useful at temperatures lower and higher than can be had with mineral base oils. However, the polyether oils cannot be used as base oils per se in grease compositions at temperatures as low as 100 F. or as high as 400 F. Polyether oils inherently are readily susceptible to oxidation at such high temperatures as 400 F. and become too viscous at such low temperatures as -100 F.

It is an object of this invention, therefore, to prepare grease compositions which are serviceable at -100 F. and at 250 F.

It is another object of this invention to prepare grease compositions from a combination of polysiloxane oils and polyether oils.

It is a further object of this invention to improve the heat stability (e. g., at temperatures as high as 400 F.) of grease compositions containing polyether base oils.

It is a still further object of this invention to prepare grease compositions which are plastic at F. and at 250 F., and which show excellent anti-wear characteristics at high temperatures.

These and further objects of this invention will be apparent from the following description and appended claims.

It has now been found that grease compositions which are plastic at low and high temperatures can be prepared by incorporating a grease thickening agent in a base oil comprising a mixture of a polysiloxane oil and a polyether oil. That is, by combining a polysiloxane oil and a polyether oil, a base oil can be obtained which can be thickened to the consistency of a grease, resulting in a grease composition which is plastic at extremely low and high temperatures. Furthermore, the addition of polysiloxane oils to polyether oils enhances the heat stability of the polyether oils.

The grease compositions of this invention not only remain plastic at extremely low and high temperatures and more heat-stable at high temperatures, but they also have excellent low wear characteristics at high temperatures. Thus, by using the grease compositions of this invention, a multi-purpose grease can be obtained which is plastic at low and high .temperatures and also exhibits low wear at high temperatures (e. g., 250 F.).

The grease compositions of this invention comprise polysiloxane oils, polyether oils, and grease thickening agents.

The polysiloxane base oils can be represented by a formula indicative of the structure of a monosiloxane.

whereinR and R represent alkyl radicals containing no more than 5 carbon atoms, aromatic radicals, alkaryl radicals or aralkyl radicals, and 11, having a value of at least 10, represents the number of monomeric units present in the polymer. R and R may or may not be alike. When R and/or R are alkaryl radicals or aralkyl radicals, the alkyl groups attached to the aromatic nucleus contain no more than 3 carbon atoms. It is particularly preferred that the polysiloxane base oil be a polymethyl polysiloxane; that is, in the above formula, that R and R both represent methyl radicals.

In the actual formation of a polysiloxane, all of the monomeric units may not have the same formula as that represented hereinabove. For example, in some of the monomeric units, there may be two R radicals attached to the silicon atom; in other monomeric units, there may be two R radicals attached to the silicon atom. However, the majority of the monomeric units are as represented in the above formula.

Examples of R and R radicals include the radicals derived from methane, ethane, propane, propene, butane, butene, pentane, pentene, benzene, anthracene, phenylmethane, phenylethane, phenylpropane, methylbenzene, ethylbenzene, propylbenzene, etc.

The polyether oils which are used herein in combination with the polysiloxane oils according to this invention are polymeric alkylene oxides and/or polymeric alkylene glycols, and may be represented by the following formula:

wherein A and B represent hydrogen, alkyl radicals containing from 1 to 12 carbon atoms, aromatic radicals, aralkyl radicals or alkaryl radicals wherein the aliphatic groups attached to the aromatic nucleus contain a total of no more than carbon atoms; A and 13 also represent ester-forming groups containing from 2 to 12 carbon atoms; :3 is a number having a value from 2 to 4; and n is a number having a Value of from 4 to 20. A and B may or may not be alike.

The polyethers may be prepared from the various alkylene oxides (e. g. ethylene oxide), the higher 1,2-epoxides (such as 1,2-propylene oxide), the alkylene glycols (e. g., ethylene glycol) and mixtures of these. The resulting products may be polyoxyallcylene diois or polyalkylene glycol derivatives; that is, the terminal hydroxyl groups can remain as such, or one or both of the terminal hydroxyl groups can be removed during the polymerization reaction or subsequent thereto, as by etherification or esterification to yield monoor di-ether or monoor di-ester groups or a combination of such terminal groups whereby certain desirable properties are imparted to the final polymeric mixtures. For example, in the above formula A and/or B may be: allryl radicals, forming a di-alkyl polyether (e. g., dibutyl heptaoxypropylene diether); ester-forming radicals, forming alkyl oxyalkylene esters (e. g., butyl pentaoxypropylene acetate); hydrogen, forming polyglycols (e. g., polyethylene glycol), etc.

To further exemplify the polyether oils which can be used, the polyether oil, that is, the (CO) 11.- section of the above formula, can be derived from such basic units asthe following oxides:

or basic units obtained by the dehydration of alkylene glycols, resulting in the formation of the following: ethylene oxide propylene oxide --(CH2CH2CH2-O)-, butylene oxide (CH2-CH2-CH2CI-I2O), etc. The molecular weight of the polyether oils used according to this invention can range from 300 to 2000, from 400 to 1000 being preferred.

The thickening agents which may be incorporated in the base oils according to this invention include metal soaps, amides, silica, bentonite, etc. For the most part, however, it is preferred to use a metal soap, preferably a monovalent metal soap such as the soaps of lithium and sodium.

The metal soap thickening agents used herein may be represented by the following formula:

wherein R represents a saturated or unsaturated alkyl group or an aralkyl group, the B group having from 10 to 30 carbon atoms, 16 to 22 carbon atoms being preferred; X represents a carboxyl group a phosphonyl group a sulfonyl group etc.; and M represents a metal of groups 1 and 2 of the periodic table. Specifically, M may be sodium, potassium, lithium, calcium, barium or strontium; however, it is preferred that M be a member of group 1 of the periodic table, sodium and lithium being particularly preferred; n represents an integer having a value of 1 or 2, depending on whether M is monovalent or divalent. When M is nionovalent, n has a value of 1; when M is divalent, n has a value of 2.

The hydrogens of the R group may be subsituted by polar groups such as chlorine, bromine, ether, hydroxy, mercapto, etc.

Examples of the organic acids which may be used in the formation of the metal salts include lauric acid, myristic acid, palmitic acid, stearic acid, hydroxy-stearic acid, oleic acid, arachidic acid, melissic acid, phenylacetic acid, cetylbenzoic acids, acids resulting from the oxidation of petroleum products (e. g., waxes), cetane sulfonic acid, dodecyl benzene sulfonic acid, dodecane phosphonic acid, and lauryl sulfuric acid. Acids of lower molecular weight, such as acetic acid and the like, may be admixed with the acids forming the thickening agents upon conversion to the metal salt, which lower molecular weight acids often beneficially modify the characteristics of the grease compositions.

The organic acid metal salt thickening agents of this invention are incorporated in the grease compositions in amounts sufficient to form a grease, such amounts as about 5 percent to about 30 percent (based on the finished composition, by weight) may be used. However, about 10 percent to about 20 percent are the preferred amounts.

Amides which are preferred as thickening agents herein are described in the I-Iotten U. S. patent application filed June 28, 1951, as follows: Serial No. 234,153 (phenylene diamides, such as N,N' acetyl stearoyl p phenylene diamide) Serial No. 234,154 (acyl ureas, such as octadecanoyl urea); and Serial No. 234,155, now abandoned (aliphatic amides, such as octadecanamide).

The polyether oils noted hereinabove also make it possible to prepare a concentrate of a metal soap in a polysiloxane oil such that the soap concentration may be as great as 50 percent by weight in a base oil consisting of a mixture of polyether oils and polysiloxane oils. For example, it is possible to prepare a grease composition containing 50 percent of a sodium soap, 25 percent polyether oil, and 25 percent polysiloxane oil. These percentage figures are by weight of the finished composition.

Thepolyether oils and the polysiloxane oils used in combination herein can be used in various ratios in the formation of base oils for the grease composition of this invention. The ratio of the polyether oil to the polysiloxane oil can have a value ranging from 1 to however, it is preferred to use ratios having values ranging from 1 to 3.

Although the greases herein can be prepared according to various methods, a method comprises heating together the polyether oil, the polysiloxane oil, and the thickening agent to a temperature of about 400 to 450 F., after which the grease composition is cooled to room temperature, then milled.

The polyether-polysiloxane base oil combination of the grease composition of this invention may also contain as much as percent of a petroleum hydrocarbon oil; for example, naphthenic base, paraffin base, mixed base mineral oils, lubricating oils derived from coal products, etc.

The grease compositions of this invention were tested to determine their eifectiveness at temperatures as low as 100 F. and as high as 250 F. the following Table I presents the grease compositions and the data obtained through various tests.

The Thin Film Test measures the ability of the grease composition to maintain grease-like characteristics, particularly, retention of pliability and resistance to oxidation under exposure of a thin film of grease to high temperatures. The test also indicates other grease characteristics, such as tendency to bleed, flake (some greases, although soft and greasy, crack and flake), and tendency to become tacky. The Thin Film Test is run as follows: The grease to be tested is coated on a metal strip. The grease coating is of uniform dimensions: inch thick, K; inch wide, and 2% inches long. This grease sample is placed in an oven at 250 F. and observed at periodic intervals until the sample no longer exists as a grease. The life of the grease is the number of hours during which the grease sample may be so heated before it loses its grease-like characteristics, that is, the time at which the test sample begins to become hard and brittle.

The Bearing Life for a particular grease composition was determined by the following test procedure which is known as the Army-Navy High Speed Bearing Test, quoted as MIL-G-3278. In this test, a ball bearing packed with grease is operated at 10,000 R. P. M. continuously for Table I Experiment No.

Composition, Percent By Weight A. Thickening Agent:

Lithium Stearate 10. Calcium Stearate 1 13. Base Oil:

Polyether PG iG 1 5g, 7

Polycther PG-61 2 Polymethyl siloxane LT 0. Secondary Additives:

Phenyl alpha naphthylamme Zinc dibutyl dithiocarbamate 2.0 2.0

Dilauryl selenide 2, 0 2, 0

Alizarin 0.1 0 1 D. Test Data:

Viscosity l00 F., 20

secr poises 4 Thin Film Life, 250 F.,

hrs 1,000 Bearing Lile, 250 F., hrs (834) (1,126) AS'IM Penetration, un-

Worked, 77 F 288 LButyl methyl heptaoxypropylene diether having a molecular Weight of 500, and a viscosity of 12000 centlstokes at 65 F. and 11.7 centistokes at 100 F.

B Butyl methyl pentaoxypropylene diether having a molecular weight of 400, and a viscosity of 2200 centistokcs at 65 F., 6.4 centistokes at 100 F. and 2.6 centistokes at 210 F.

3 A polymetliyl siloxane having a viscosity of 255 centistokes at 65 F., 20 centistokes at 100 F. and 9.3 centistokes at 210 F.

i The viscosities presented herein are obtained according to the following procedure, which is a slight modification of the ASTM Method No. D-1092-50T:

A grease sample was forced through a metal capillary tube at a constant pressure, and the rate of flow through the capillary tube was measured. Through the use of the formula:

capillary tube and v/t=flow rate, the viscosity was determined in poises at various shear rates.

It is preferred that grease compositions of this invention have viscosities at 100 P. less than 10,000 poises at 20 reciprocal seconds shear rate.

In addition to the base oils and the thickening agents, the grease compositions of this invention may also include stringiness agents, oxidation inhibitors, anti-wear agents, extreme pressure agents, peptizing agents, fillers, anti-thixotropic agents, etc.

We claim:

1. A grease composition comprising a mixture of a polysiloxane oil and a polyoxyalkylene oil, and a grease thickening agent in an amount sufficient to thicken the oil mixture to the consistency of a grease said polyoxyalkylene oil being present in an amount sufficient to improve the dispersibility of said thickening agent in said polysiloxane oil.

2. A grease composition comprising a base oil consisting essentially of a polyoxyalkylene oil and a polysiloxane oil, wherein the ratio of the polyoxylalkylene oil to the polysiloxane oil has a value ranging from 1 to 10, and a small amount, sufficient substantially to thicken the base oil to the consistency of a grease, of a grease thickening agent.

3. A grease composition comprising a base oil consisting essentially of a polyoxyalkylene oil and a polysiloxane oil, wherein the ratio of the polyoxyalkylene oil to the polysiloxane oil has a value ranging from 1 to 3, and a small amount, suflicient substantially to thicken the base oil to 7 the consistency of a grease, of a grease thickening agent.

4. The grease composition of claim 3, wherein the polyoxyalkylene oil has a molecular weight ranging from 400 to 2000.

5. The grease composition of claim 3, wherein the polyoxyalkylene oil has the formula A-O- (:00) 11.B

wherein A and B are selected from the group consisting of hydrogen, alkyl radicals, aromatic radicals, and ester-forming radicals, a: is a number having a value from 2 to 4, and n is a number having a value from 4 to 20.

6. The grease composition of claim 3, wherein the polysiloxane oil has the formula represented by a monosiloxane as follows:

wherein R and R. are selected from the group consisting of alkyl radicals, aromatic radicals, alkaryl radicals and aralkyl radicals, and n is a number at least 10.

'7. The grease composition of claim 3, wherein the thickening agent is a metal soap.

8. The grease composition of claim 3, wherein the thickening agent is a monovalent metal soap.

9. The grease composition of claim 3, wherein the polysiloxane oil is a polymethyl siloxane, the polyoxy alkylene oil is a polypropylene oxide oil and the thickening agent is an alkali metal soap of a fatty acid.

10. The grease composition of claim 3, wherein the polysiloxane oil is a polymethylsiloxane.

11. A grease composition having a viscosity of less than 10,000 poises at 100 F. at 20 reciprocal seconds shear rate, said composition comprising a mixture of a polysiloxane oil and a polyoxy- 4o alkylene oil, and a grease thickening agent in an amount suiiicient to thicken the oil mixture to the consistency of a grease said polyoxyalkylene oil being present in an amount sufficient to improve the dispersibility of said thickening agent in said polysiloxane oil.

12. A grease composition having a viscosity of less than 10,000 poises at 100 F. at 20 reciprocal seconds shear rate, said composition comprising a mixture of a polymethylsiloxane oil and a polypropylene oxide oil, and from 5 to by weight, of an alkali metal soap of a fatty acid, said polypropylene oxide oil and polymethylsiloxane oil being present in a ratio having a value of from 1 to 10.

13. A grease composition having a viscosity of less than 10,000 poises at l00 F. at 20 reciprocal seconds shear rate, said composition comprising a mixture of a polymethylsiloxane oil and a polypropylene oxide oil, and from 10 to 20%, by weight, of an alkali metal soap of a fatty acid, said polypropylene oxide oil and polymethylsiloxane oil being present in a ratio having a value of from 1 to 10.

14. A grease composition having a viscosity of less than 10,000 poises at l00 F. at 20 reciprocal seconds shear rate, said composition comprising a mixture of a polymethylsiloxane oil and a polypropylene oxide cil, and from 10 to 20%, by weight, of an alkali metal soap of a fatty acid, said polypropylene oxide oil and polymethylsiloxane oil being present in a ratio having a value of from 1 to 3.

15. A grease composition comprising a base oil mixture comprising a polymethylsiloxane oil and a polypropylene oxide oil and from 5 to of a thickening agent, the ratio of said polymethyl siloxane oil and polypropylene oxide oil having a value of 1.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,551,931 Currie May 8, 1951 2,577,706 Hotten Dec. 4, 1951 2,585,182 Sterman Feb. 12, 1952 

1. A GREASE COMPOSITION COMPRISING MIXTURE OF A POLYSILIOXANE OIL AND A POLYOXYALKYLENE OIL, AND A GREASE THICKENING AGENT IN AN AMOUNT SUFFICIENT TO THICKEN THE OIL MIXTURE TO THE CONSISTENCY OF A GREASE SAID POLYOXYALKYLENE OIL BEING PRESENT IN AN AMOUNT SUFFICIENT TO IMPROVE THE DISPERSIBILITY OF SAID THICKENING AGENT IN SAID POLYSILOXANE OIL. 